At least an embodiment of the present invention generally relates to a rotary transmitting assembly, a device for converting rotary motion to linear motion, and a motor. More specifically, at least an embodiment of the present invention relates to a rotary transmitting assembly, a device for converting rotary motion to linear motion, and a motor that provide a secure positioning of axially and radially loaded components thereof in an axial and radial direction.
A known type of a device for converting rotary motion of a motor into linear motion includes a conventional ball nut for transmitting the rotary motion of a rod member to a linear motion, wherein the ball nut is movably arranged on the rod member. Since the ball nut is moved back and forth on the rod member, the bearings for supporting the rod member with respect to a housing are under high axial and radial load.
One example of a device for converting rotary motion into linear motion is disclosed in JPB4722247. However, JPB4722247 discloses a conventional bearing arrangement for rotatably supporting the rotational portion on the stationary portion (i.e., housing), wherein the components for supporting the rotational portion to the stationary portion are easy to come off under high axial and radial load.
An object of the invention is to increase the secure positioning of loaded components in a rotary transmitting assembly in an axial and radial direction. A further object of the invention is to reduce the axial runout. An even further object of the invention is to prevent rod member movement in the axial direction with a rotary transmitting assembly.
In view of the state of the known technology and in accordance with a first embodiment of the present invention, a rotary transmitting assembly is provided that basically comprises a housing, a hollow shaft, a rod member, at least one bearing, and a stopper member. The hollow shaft is coupled to the housing rotatably around a first rotation axis. The hollow shaft has at least one outer circumferential stepped shaft portion and at least one inner circumferential stepped shaft portion. The rod member is coupled to the housing rotatably around the first rotation axis having at least one contacting portion and at least one protruding part. The at least one contacting portion contacts the at least a part of the hollow shaft in a radial direction and the at least one protruding part abuts the at least one inner circumferential stepped shaft portion in an axial direction. The at least two contact points, although preferably closely arranged to each other, but also can be arranged apart from each other. The at least one bearing comprises at least one circular inner support part and at least one circular outer support part supporting the hollow shaft and the rod member to the housing rotatably around the first rotation axis. The at least one circular inner support part abuts at least a part of the at least one outer circumferential stepped shaft portion in the axial direction and the at least one circular outer support part abuts a bearing surface of the housing in the axial direction. The stopper member is fixed to the rod member, wherein the stopper member abuts the at least one circular inner support part in the axial direction.
Because the stopper member receives the at least one circular inner support parts of the bearing and the at least one outer circumferential stepped shaft portion receives the other one of the circular inner support parts of the bearing, the axial runout is reduced. This axially fixing arrangement further enables that rod member movement in an axial direction is prevented.
Preferably, the rotary transmitting assembly further comprises a circular bearing holding member fixed to an inner surface of an opening portion of the housing and configured to abut at least a part of the at least one circular outer support part in the axial direction. This further enables a secure fixture and positioning of the bearing in an axial direction.
Preferably, the rotary transmitting assembly is configured so that an outer diameter of the circular bearing holding member is larger than an outer diameter of the at least one circular outer support part in a radial direction. This enables a secure fixture and positioning of the bearing in an axial direction.
Preferably, the rotary transmitting assembly is configured so that the circular bearing holding member comprises at least one sealing element. This enables secure sealing.
Preferably, the rotary transmitting assembly is configured so that the circular bearing holding member is securely fixed to the inner surface of the opening portion of the housing, in particular at least one part of the circular bearing holding member is swaged to at least one part of the opening portion and a deformed portion is formed. Therefore, the circular bearing holding member securely locks the bearing.
Preferably, the rotary transmitting assembly is configured so that the circular bearing holding member has a concave portion on an upper surface of the circular bearing holding member and a convex portion on a lower surface of the circular bearing holding member, wherein the concave portion has a tool engaging hole, and wherein the convex portion on the lower surface of the circular bearing holding member is arranged in the deeper area than the deformed portion in the axial direction. This arrangement enables that the stress from the swag/deformation can escape to the convex portion of the circular bearing holding member. With this structure, the circular bearing holding member is securely fixed to the housing. This structure is an effective bearing fixing assembly. Since the circular bearing holding member can be threadedly engaged with the inner surface of the opening portion of the housing and/or swaged to at least one part of the opening portion forming the deformed portion, this structure has a high flexibility to dimension tolerances of the bearing and/or the housing.
Preferably, the rotary transmitting assembly is configured so that the housing has at least one stepped housing section, wherein the at least one bearing is arranged in the manner where an axial end surface of the at least one bearing is positioned between the outer surface of the at least one stepped housing section and the inner surface of the at least one stepped housing section. With this structure, a sufficient thickness of the housing is provided for securing the bearing in a radial direction.
Preferably, the rotary transmitting assembly is configured so that the at least one bearing is a four-point contact bearing, wherein the circular inner support part has a lower inner support part and an upper inner support part, wherein the lower inner support part abuts the at least one outer circumferential stepped shaft portion and the upper inner support part abuts the stopper member. Because the stopper member receives the upper inner support part of the bearing and the at least one outer circumferential stepped shaft portion receives lower inner support part of the bearing, the axial runout is reduced. This axial locking arrangement further enables that rod member movement in an axial direction is prevented. The circular outer support part may also comprise two separate support parts, i.e., an upper outer support part and a lower outer support part.
Preferably, the rotary transmitting assembly is configured so that at least one portion of the hollow shaft corresponds to the shape of the at least one contacting portion of the rod member, wherein the at least one contacting portion of the rod member may have a shape different to a circular shape, in particular, the at least one contacting portion of the rod member may has at least either one of a polygonal shape, an ellipse shape, and a shape with a concave section and/or convex section. This rotation transmitting structure conveys the rotation of the hollow shaft to the rod member.
In accordance with another embodiment of the present invention, a device for converting rotary motion to linear motion is provided that basically comprises a housing, a stator, a hollow shaft, a plurality of magnets, a rod member, at least one bearing, a stopper member, and a ball nut. The stator with a plurality of coils is arranged in a circumferential direction, wherein the stator is disposed on a cylindrical portion of the housing. The hollow shaft is coupled to the housing rotatably around a first rotation axis, wherein the hollow shaft has at least one outer circumferential stepped shaft portion and at least one inner circumferential stepped shaft portion. A plurality of magnets is disposed on a circumferential outer surface of the hollow shaft inwardly from the stator in a radial direction. The rod member is coupled to the housing rotatably around the first rotation axis having at least one contacting portion and at least one protruding part, wherein the at least one contacting portion contacts at least a part of the hollow shaft in a radial direction and the at least one protruding part abuts the at least one inner circumferential stepped shaft portion in an axial direction. The at least one bearing comprises at least one circular inner support part and at least one circular outer support part supporting the hollow shaft and the rod member to the housing rotatably around the first rotation axis. The at least one circular inner support part abuts the at least a part of the at least one outer circumferential stepped shaft portion in the axial direction and the at least one circular outer support part abuts a bearing surface of the housing in the axial direction. The stopper member is fixed to the rod member, wherein the stopper member abuts the at least one circular inner support part in the axial direction. The ball nut is rotatably supported on spiral grooves on an outer circumferential periphery of the rod member, wherein the ball nut moves in the axial direction of the first rotation axis in accordance with rotation of the rod member.
The ball nut moves back and forth in an axial direction, thus, the bearing is under a high load in the axial direction of the rod member. Because the stopper member receives one of the circular inner support parts of the bearing and the at least one outer circumferential stepped shaft portion receives the other one of the circular inner support parts of the bearing, the axial runout is reduced. This axial locking arrangement further enables that rod member movement in an axial direction is prevented.
In accordance with another embodiment of the present invention, a motor is provided that basically comprises a device for converting rotary motion to linear motion according to one of the above embodiments of the invention. This motor can achieve enough strength against the force of the hollow shaft and rod member in both radial and axial direction.
Preferably, the motor is configured so that the motor is formed as a braking system motor. In a braking system, this motor is used to change pressure of a brake booster that the ball nut is mounted to. And the smooth and quick change of pressure is required for safe and comfortable ride. Then the ball nut is required to be able to move back and force with good response and the bearing is under specially high pressure in an axial direction due to such movement.
The advantages of at least an embodiment of the present invention can be summarized as follows:                a. The stability of fixation and positioning of loaded components is increased in an axial and radial direction.        b. The axial runout is reduced.        c. The rod member movement in the axial direction is prevented.        
Further advantages that can be obtained with embodiments can be summarized as follows:                a. The circular bearing holding member securely locks the bearing. This structure is an effective bearing fixing assembly.        b. The structure has a high flexibility in the standpoint of dimension tolerances of the bearing and/or the housing.        c. Sufficient thickness of the housing is provided for sustaining the bearing in a radial direction.        d. The rotation transmitting structure conveys the rotation of the hollow shaft to the rod member.        e. The motor can achieve enough strength against the force of the hollow shaft and rod member in both radial and axial direction.        
Also other objects, features, aspects and advantages of the disclosed rotary transmitting assembly, the device converting rotary motion to linear motion, and the motor will become apparent to those skilled in the art from the following detailed description.